There is more than the cost of gas to worry about if one intends to run their Onan 5500 24/7.
Here's some of the periodic maintenance Onan recommends for the Onan 5500:
Replace oil and oil filter every 150 hours (or every 6.25 days of 24/7 runtime).
Replace air filter every 150 hours (or every 6.25 days of 24/7 runtime).
Replace spark plugs and fuel filter every 450 hours (or every 18.75 days of 24/7 runtime)
Adjust valve lash every 450 hours (or every 18.75 days of 24/7 runtime).
Filter (oil, air, and fuel) and oil changes on the Onan 5500 aren't very difficult.
Anyone replace spark plugs on a 5500? Difficult?
What about adjusting the valves. Do you have to remove the generator to get access to the valves?